Recently, hydrogen has attracted attention as alternative energy to oil. For high-pressure hydrogen equipment such as pressure accumulators or pipes for storing and supplying hydrogen at a high pressure, there is a demand for materials exhibiting high resistance to high-pressure hydrogen at low cost. However, most metal materials exhibiting brittleness (=hydrogen environment brittleness) to high-pressure hydrogen gas and even materials exhibiting slight hydrogen environment brittleness to hydrogen have to be actually used for economical reasons. Such materials should be verified to be safe in practical use.
A drawing qualitatively showing fatigue crack growth characteristics in high-pressure hydrogen gas is shown in NPL 1 or the like.
A method and a procedure of selecting a material to be used and limiting a usage count, a lifetime, and the like thereof on the basis of test data in a hydrogen gas environment for materials likely to be embrittled in the high-pressure hydrogen gas are disclosed in NPL 2, and the procedure is shown in FIG. 12. In this method, a delayed crack test method of driving a bolt or a wedge into a block with a crack formed therein to load the block, maintaining the resultant block for 1000 hours or more, and acquiring a crack-growth threshold stress intensity factor KIH-H is performed (step s101). A fracture-limit crack depth ac of equipment is acquired from the crack-growth threshold stress intensity factor KIH-H (step s102) and an initially-estimated crack depth a0 is calculated from the inspection limit (step s103).
Subsequently, a fatigue crack growth test in high-pressure hydrogen is performed in conditions of arbitrary repetition cycle times or literature data is acquired (step s104). Conditions of pressure P and stress ratio R (minimum load/maximum load) of actual equipment are set (step s105). Subsequently, a fatigue crack growth analysis is performed on area I, that is, a section of (1−R)×K0(a0) to (1−R)×KIH-H(ac), in the da/dN-ΔK diagram obtained in step s104 (step s106). From this analysis result, the fatigue crack lifetime (repetitive filling lifetime) until the initially-estimated crack depth a0 reaches the fracture-limit crack depth ac or the depth corresponding to 80% of the plate thickness is calculated (step s107). It is determined that the equipment can be safely used when the lifetime is larger than the usage count (YES in step s107), and it is determined that a crack inspection should be carried out or use thereof should be stopped when the usage count reaches the lifetime (NO in step s107). The same test method as described above is disclosed in NPL 3.